The present invention relates to a multipoint communication system in which a broadcast channel is established from a central station to each of a plurality of terminal stations and a multiple access channel is established from each terminal station to the central station, the central station polling the terminal stations in succession asking the polled stations to transmit.
In a multipoint communication system, the central station sends polling messages one by one to the terminal stations, asking the polled stations to transmit. If the polled station has a data signal to transmit, it goes ahead; if not, a negative reply, or absence of reply, is received by the central station, which then polls the next terminal station in sequence. However, this constant exchange of control messages between the central and terminal stations is not efficient if the round-trip propagation delay is large as in the satellite communication system.